Metal particles and method for producing same

ABSTRACT

The present invention provides metal particles, in which microfine carbon fibers are uniformly dispersed, and a method of producing such metal particles. The method comprises the steps of: electrolyzing an electrolytic solution, in which the microfine carbon fibers are dispersed, so as to deposit metal particles, in which the microfine carbon fibers are incorporated, on a cathode; and separating the deposited metal particles from the cathode. The separated metal particles are collected, cleaned and dried.

FIELD OF TECHNOLOGY

The present invention relates to metal particles suitable for powder metallurgical materials, electric contact points, battery, electromagnetic interference shield materials, electric conductive materials, contact points of frictional members, slide members, etc. and a method of producing the metal particles.

BACKGROUND TECHNOLOGY

Composite materials, in which carbon nano tubes or carbon nano fibers (hereinafter referred to as microfine carbon fibers) are dispersed, are known.

A block-shaped composite material disclosed in Japanese Patent Gazette No. 2000-223004 is formed by mixing microfine carbon fibers with metal powders and sintering the mixture.

Diameters of the microfine carbon fibers are extremely small, e.g., 5-50 nm; on the other hand, diameters of ordinary metal powders are 200-1000 nm, so diameters of metal powders are 10 times greater than those of fine carbon fibers. They cannot be uniformly mixed by merely mixing them.

Conventionally, firstly the metal powders are melted in an acid solution. For example, copper powders are melted in an acid solution, e.g., hydrochloric acid, sulfuric acid, nitric acid. Then, the micro fine carbon fibers are dispersed in the solution, the mixture is dried and sintered to gain the composite material.

However, the conventional method of producing the composite material has following disadvantages: the steps of melting the metal powders, drying the mixture and sintering the mixture are very troublesome; it takes a long time; and production costs must be high. Further, it is difficult to uniformly disperse a large amount of microfine carbon fibers.

The present invention has been invented to solve the problems of the conventional technology. An object of the present invention is to provide metal particles, in which microfine carbon fibers are uniformly dispersed, and a method of producing the metal particles.

DISCLOSURE OF THE INVENTION

The method of producing metal particles of the present invention comprises the steps of: electrolyzing an electrolytic solution, in which the microfine carbon fibers are dispersed, so as to deposit metal particles, in which the microfine carbon fibers are incorporated, on a cathode; and separating the deposited metal particles from the cathode.

The method may further comprise the steps of collecting, cleaning and drying the separated metal particles.

In the method, conditions of said electrolyzing step may be adjusted so as to deposit the metal particles having average particle diameters of several hundred nm to several dozen micro meter.

In the method, the metal particles may be copper particles.

In the method, the metal particles may be separated by soaking the cathode, on which the metal particles are deposited, into acetone and applying supersonic waves.

In the method, the metal particles may be separated from the cathode by spraying compressed air to the cathode or applying shocks or vibrations to the cathode while electrolylzing.

In the method, the microfine carbon fibers may be dispersed in the electrolytic solution by adding a dispersing agent, which is made from an organic compound.

In the method, the dispersing agent may be polyacrylic acid whose molecular weight is 5000 or more.

In the method, a surface of the cathode may be roughed.

The metal particle of the present invention is produced by the method of the present invention.

Further, a composite material can be produced by melting an aggregate of the metal particles of the present invention.

Note that, an aqueous solution, a melted salt and an ionic liquid may be used as the electrolytic solution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scanning electron micrograph of metal particles of Experiment 1, which are deposited on a cathode;

FIG. 2 is an enlarged view of FIG. 1;

FIG. 3 is a scanning electron micrograph of metal particles of Experiment 2, which are deposited on the cathode;

FIG. 4 is an enlarged view of FIG. 3;

FIG. 5 is a scanning electron micrograph of metal particles of Experiment 3, which are deposited on the cathode;

FIG. 6 is a scanning electron micrograph of metal particles of Experiment 4, which are deposited on the cathode;

FIG. 7 is a scanning electron micrograph of metal particles of Experiment 5, which are deposited on the cathode;

FIG. 8 is a scanning electron micrograph of metal particles of Experiment 6, which are deposited on the cathode; and

FIG. 9 is a scanning electron micrograph of metal particles of Experiment 7, which are deposited on the cathode.

PREFERRED EMBODIMENTS OF THE INVENTION

Preferred embodiment of the present invention will now be described.

In the present invention, the method of producing metal particles is characterized by the steps of: electrolyzing an electrolytic solution, in which the microfine carbon fibers are dispersed, so as to deposit metal particles, in which the microfine carbon fibers are incorporated, on a cathode; and separating the deposited metal particles from the cathode.

Further, the separated metal particles are collected, cleaned and dried.

Metal particles, whose average particle diameters are several hundred nm to several dozen micro meter, can be deposited by adjusting conditions of the electrolyzing step, e.g., current density, electrolyzing time.

Optimum current density is selected on the basis of particle diameters, production efficiency, etc.

In case of mass production, for example, a copper electrolytic solution, whose main components are copper sulfate and sulfuric acid, is stored in an electrolytic bath, then CNTs (carbon nano tubes) or CNFs (carbon nano fibrers) are added to the electrolytic solution with an organic compound, which acts as a dispersing agent. An anode is made of electrolytic copper so as to supply copper ions to the electrolytic solution. Note that, the anode may be made of other metals, e.g., lead, and copper ions may be supplied from the outside.

In some cases, the electrolytic solution is agitated by suitable means, e.g., pump, while electrolyzing, and concentration of the solution and a ratio of the components therein are controlled.

The metal particles deposited on the cathode are separated therefrom by soaking the cathode, on which the metal particles have been deposited, into acetone and applying supersonic waves.

Note that, the metal particles may be separated from the cathode by spraying compressed air to the cathode or applying shocks or vibrations to the cathode while electrolyzing the electrolytic solution.

Particle diameters and toughness of the metal particles and easiness of separating from the cathode may be adjusted by adding organic or inorganic compounds, e.g., thiourea, gelatin, tungsten, chlorides, to the electrolytic solution.

Preferably, the cathode is made of titanium, which is easily separated from the metal particles deposited thereon. Further, a surface of the cathode may be roughed so as to easily form the deposited metal into particles. For example, fine projections of niobium, tantalum or platinum may be formed on the surface of the titanium cathode.

To disperse microfine carbon fibers in the electrolytic solution, a dispersing agent, which is made from an organic compound, is added to the solution. For example, a preferable dispersing agent is polyacrylic acid whose molecular weight is 5000 or more.

Particle diameters of the metal particles including CNTs or CNFs are determined by concentration of metal ions in the electrolytic solution, current density for electrolyzing the solution, fiber diameters and lengths of the CNTs or CNFs. Note that, the metallic component of the metal particles is not limited to copper.

Various composite materials can be made by melting aggregates of the metal particles. In this case, various additives may be added to the metal particles to produce composite materials.

For example, the metal particles including the microfine carbon fibers and metal particles including no microfine carbon fibers may be mixed with a proper mixture ratio so as to produce a composite material including a desired amount of the microfine carbon fibers.

Further, the metal particles may be mixed with resin, etc.

The composite materials may be produced by resin molding, sintering, metal injection molding, etc.

As described above, particle diameters of the metal particles are several hundred nm to several dozen micro meter, further the microfine carbon fibers are incorporated into the metal particles. Therefore, the microfine carbon fibers can be uniformly mixed in a composite material, which is produced by melting an aggregates of the metal particles.

By varying an amount of the microfine carbon fibers dispersed in the electrolytic solution and the electrolyzing conditions, various types of metal particles, which include different amounts of microfine carbon fibers and have different particle diameters, can be produced; therefore, the amount of microfine carbon fibers included in the composite material, which is produced by melting the aggregates of the metal particles, can be optionally controlled.

Since CNTs and CNFs have high slidability, high electric conductivity and high heat conductivity, the composite material may be used as materials of slide bearings, electrodes, electric contact points, heat sinks, etc.

Experiment 1

Electrolytic Solution CuSO₄.5H₂O: 0.85M H₂ SO₄: 0.55M PA5000 2 × 10⁻⁵M CNF: 2 g/L (Note, PA5000 is polyacrylic acid whose molecular weight is 5000; and CNF is carbon nano fiber.)

The electrolytic solution was agitated and electrolyzed for 5 minutes with solution temperature of 25° C. and current density of 5 A/dm²; scanning electron micrographs of a film deposited on the surface of the cathode are shown in FIGS. 1 and 2. As shown in FIGS. 1 and 2, sea urchin-shaped Cu-CNF compounds, in which many CNFs were incorporated in fine spherical copper particles having diameters of about 2-3 micro meter, were produced. The compounds were easily separated from the cathode and formed into particles by spraying compressed air to the cathode or applying supersonic waves to the cathode in acetone.

Experiment 2

Electrolytic Solution CuSO₄.5H₂O: 0.85M H₂ SO₄: 0.55M PA5000 2 × 10⁻⁵M CNF: 2 g/L (Note, PA5000 is polyacrylic acid whose molecular weight is 5000; and CNF is carbon nano fiber.)

The electrolytic solution was agitated and electrolyzed for 20 minutes with solution temperature of 25° C. and current density of 5 A/dm²; scanning electron micrographs of a film deposited on the surface of the cathode are shown in FIGS. 3 and 4. As shown in FIGS. 3 and 4, sea urchin-shaped Cu-CNF compounds, in which many CNFs were incorporated in fine spherical copper particles having diameters of about 10-30 micro meter, were produced. The compounds were easily separated from the cathode and formed into particles by spraying compressed air to the cathode or applying supersonic waves to the cathode in acetone.

According to Experiments 1 and 2, the particle-shaped compounds can be produced with higher current density. Further, sizes of them can be controlled by adjusting an electrolyzing condition (electrolyzing time).

Experiment 3

Electrolytic Solution CuSO₄.5H₂O: 220 g/L H₂ SO₄: 55 g/L PA5000 0.25 g/L CNF: 10 g/L (Note, PA5000 is polyacrylic acid whose molecular weight is 5000.)

The electrolytic solution was agitated and electrolyzed for 10 minutes with solution temperature of 25° C. and current density of 40 A/dm²; a scanning electron micrographs of a film deposited on the surface of the cathode is shown in FIG. 5. As shown in FIG. 5, sea urchin-shaped Cu-CNF compounds, in which many CNFs were incorporated in fine spherical copper particles having diameters of about 10-30 micro meter, were produced. Amount of CNFs included in the compounds was about 7 vol %.

Experiment 4

Electrolytic Solution CuSO₄.5H₂O: 220 g/L H₂ SO₄: 55 g/L PA5000 0.25 g/L CNF: 20 g/L

The electrolytic solution was agitated and electrolyzed for 10 minutes with solution temperature of 25° C. and current density of 40 A/dm²; a scanning electron micrographs of a film deposited on the surface of the cathode is shown in FIG. 6. As shown in FIG. 6, sea urchin-shaped Cu-CNF compounds, in which many CNFs were incorporated in fine spherical copper particles having diameters of about 10-30 micro meter, were produced. Amount of CNFs included in the compounds was about 15 vol %.

According to Experiments 3 and 4, the amount of CNFs incorporated in the Cu-CNF compounds can be increased by increasing amount of CNFs in the electrolytic solution.

Experiment 5

Electrolytic Solution CuSO₄.5H₂O: 1 g/L H₂ SO₄: 150 g/L polyoxyethylene (10) octylphenyl ether 2 g (dispersing agent) CNF: 20 g/L

The electrolytic solution was agitated and electrolyzed for 10 minutes with solution temperature of 25° C. and current density of 10 A/dm²; a scanning electron micrographs of a film deposited on the surface of the cathode is shown in FIG. 7. In this experiment, activity of outer faces of CNFs are higher than that of CNFs used in Experiments 1-4. By using such active CNFs, Cu-CNF compounds, in which coppers stuck on surfaces of CNFs like beads (or rosary) as shown in FIG. 7, was produced.

Experiment 6

Electrolytic Solution CuSO₄.5H₂O: 1 g/L H₂ SO₄: 50 g/L polyoxyethylene (10) octylphenyl ether 2 g (dispersing agent) CNF: 20 g/L

The electrolytic solution was agitated and electrolyzed for 10 minutes with solution temperature of 25° C. and current density of 40 A/dm²; a scanning electron micrographs of a film deposited on the surface of the cathode is shown in FIG. 8. In this experiment, activity of outer faces of CNFs are higher than that of CNFs used in Experiments 1-4. By using such active CNFs, Cu-CNF compounds, in which coppers stuck on surfaces of CNFs like branches as shown in FIG. 8, was produced.

Experiment 7

Electrolytic Solution NiSO₄.6H₂O: 250 g/L NiCl₂.6H₂O: 45 g/L H₃ BO₃: 35 g/L CNF: 10 g/L PA5000 0.5 g/L

The electrolytic solution was agitated and electrolyzed for 10 minutes with solution temperature of 25° C. and current density of 40 A/dm²; a scanning electron micrographs of a film deposited on the surface of the cathode is shown in FIG. 9. Namely, CNF compound powders can be produced with metals other than copper, which can be deposited.

EFFECTS OF THE INVENTION

By the present invention, extremely fine metal particles, whose diameters are several hundred nm, and treatable metal particles, whose diameters are several dozen micro meter, can be optionally produced, and amount of microfine carbon fibers incorporated in the metal particles can be controlled. 

1. A method of producing metal particles comprising the steps of: electrolyzing an electrolytic solution, in which the microfine carbon fibers are dispersed, so as to deposit metal particles, in which the microfine carbon fibers are incorporated, on a cathode; and separating the deposited metal particles from the cathode.
 2. The method according to claim 1, further comprising the steps of collecting, cleaning and drying the separated metal particles.
 3. The method according to claim 1, wherein conditions of said electrolyzing step are adjusted so as to deposit the metal particles having average particle diameters of several hundred nm to several dozen micro meter.
 4. The method according to claim 1, wherein the metal particles are copper particles.
 5. The method according to claim 1, wherein the metal particles are separated by soaking the cathode, on which the metal particles are deposited, into acetone and applying supersonic waves.
 6. The method according to claim 1, wherein the metal particles are separated from the cathode by spraying compressed air to the cathode or applying shocks or vibrations to the cathode while electrolyzing.
 7. The method according to claim 1, wherein the microfine carbon fibers are dispersed in the electrolytic solution by adding a dispersing agent, which is made from an organic compound.
 8. The method according to claim 7, wherein the dispersing agent is polyacrylic acid whose molecular weight is 5000 or more.
 9. The method according to claim 1, wherein a surface of the cathode is roughed.
 10. A metal particle produced by the method according to claim
 1. 11. A composite material produced by melting an aggregate of the metal particles according to claim
 10. 